1. Field of the Invention
This invention generally relates to cable conduit devices, and more particularly to a fire-rated feed-through fitting for transferring insulated wires through a concrete floor of a building, which fitting is characterized by a non-rigid mechanical coupling in the thermal path through the fitting. This invention further relates to a method of making a non-rigid mechanical fitting coupling.
2. Description of the Prior Art
Modern office buildings are typically multi-floor structures in which each floor is formed of a concrete slab. Typically with this form of structure, it has been customary to transmit power and telecommunications signals from floor to floor through openings provided in each floor for that purpose. Thus, it has been customary to form openings in the concrete floors, to insert a feed-through fitting through the opening, to pass the wires through the feed-through fitting from the opposite face of the floor to the top face of the floor, and to make connection to an electrical outlet mounted over the opening on the top face of the floor. While this technique for wiring a building is perfectly satisfactory from the standpoint of achieving the requisite wiring interconnections throughout the building, nevertheless it has been found that the ability of the building to contain a fire which may have been started on one floor is compromised as a result of the tendency of the fire to spread through the feed-through openings to adjacent floors.
Prior art feed-through fittings have included a head assembly mounted over the floor opening, a conduit secured to the head assembly and inserted in the floor opening, and a bottom face receptacle secured to the conduit and abutting the bottom face of the floor such that the floor is in effect clamped between the head assembly and the bottom face receptacle, thereby maintaining the entire assembly in place. Additionally, it has been known to separate the feed-through conduit into two sections and to dispose between the conduit sections an intumescent barrier which expands upon subjection to heat to block the opening and thereby retard the spread of fire and smoke through the opening. Similarly, intumescent barriers have also been disposed within the conduit itself to likewise prevent the spread of fire and smoke through the conduit. In spite of these precautions, however, it has been found that the heat generated by a fire is often of such intensity that the intumescent barrier is itself incinerated, thereby losing its effectiveness. Furthermore, since the conduit sections are formed of a metal, and are typically rigidly secured to the head assembly by bolts, nuts or other rigid means, the prior art fittings serve as an excellent thermal conductor of heat between floors, further aggravating the fire containment problem.
Typical feed-through insertion fittings of the prior art are disclosed in U.S. Pat. Nos. 3,751,576; 3,803,341; 3,864,883; 3,995,102; and 4,099,020. See also Abrams et al, "Fire Tests of Poke-Through Assemblies", Fire Journal, May, 1971, pp. 56-67 for an overview of the prior art.